Hong Kong student activist Joshua Wong Chi-fung on Wednesday recounted his 12 hours of solitary confinement in a Bangkok airport at the hands of Thai police officers after they confiscated his passport on the orders of the Chinese government upon his arrival for a democracy speech.

“I did not understand the Thai officers’ English well but there was one word I heard clearly – blacklist,” the 19-year-old student said after being sent back to Hong Kong on Wednesday.